Preparation of alkyl halides



Patented Dec. 11, 1934 V 1,983,542

PREPARATION OF ALKYL HALIDES Lee Cone Holt, Edge Moor, and Herbert Wilkens Daudt, Wilmington, DeL, assignors to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application July 27, 1932, Serial No. 625,194

14 Claims. (Cl. 260-162) This invention relates to alkyl halides, more the equilibrium concentration at the reaction particularly chlorides in which the alkyl group temperature. contains less than four carbon atoms, and a proc- While the invention is susceptible of consideress for the manufacture thereof. able variation and modification in the manner It is known that alkyl halides, such as ethyl of its practical application particularlyas regards 5 chloride, have been prepared by passing hydrogen proportions of materials and the exact method chloride and a corresponding alcohol through an of procedure, the following examples will illusaqueous solution of a metal chloride such as, for trate how it may be practiced. The parts are I example, zinc chloride or ferric chloride, heated by weight.

to a temperature between 100 and 150 C. In Example I this process as previously operated, it has been customary to allow the reaction to proceed in Sixteen parts of solid zinc chloride were charged such a manner that the concentration of the into a well-insulated corrosion resistant vessel metal chloride solution reaches equilibrium. That and 6.8 parts of water added giving a solution is to say, since water is a product of the reachaving a concentration of about 70%. The tem- 15 tion and the temperature of the metal chloride perature of this solution was raised to about 13'?- solution is maintained constant throughout the 138 C. and maintained for a period of eight hours operation, after the process is under way a state during which time there was introduced into the of equilibrium is eventually established in which solution at a rate as uniform as possible, 28.57

the concentration of the metal chloride solution parts of 92.5% ethyl alcohol in the form of vapor 20 (1088 no C n pp y- In producing e y and 23.2 parts of gaseous hydrogen chloride. Chloride by this method y P g ethyl alcohol The gases evolved from the surface of the reand hydrogen chloride through a zinc chloride action liquid and consisting largely of ethyl solution maintained at a temperature of about chloride, water, hydrochloric acid and some alco- 135-140" C., we have obtained equilibrium conhol were recovered continuously and passed 25 centrations in the zinc chloride solution of the through a condenser maintained at a temperature order of about 80% zinc chloride. Since the resufiicient to condense the water vapors. During action is exothermic, difiiculty has been eX- the run, water from the condenser was returned perienced in maintaining the desired reaction to the zinc chloride solution in order to maintemperature and in order to do this it has been tain the volume and concentration thereof con- 30 customary to employ external artificial cooling stant,

means.

The present invention has for an object the Example H provision of a new and improved process for pro- Into a well-insulated corrosion resistant vessel ducing alkyl halides. A further object is the there was charged about 22.8 parts of a solu- 35 provision of a new and improved process for protion of zinc chloride having a concentration of ducing methyl, ethyl and propyl chlorides. A about 70% zinc chloride by weight. The temstill further object is to produce ethyl chloride by perature of this solution was raised to about a reaction which proceeds smoothly with higher 138-140 C. and maintained for a period of -10 yields than have heretofore been obtainedin comtwenty hours, during which time there was ini0 mercial operations. troduced into the solution, at a rate as uniform Another object is the provision of an autotheras possible, about 54.8 parts of 92.5% ethyl alcomal process for producing ethyl chloride that is, hol in the form of vapor and about 55.4 parts of a process of such character that after the regaseous hydrogen chloride having a purity of action is started it may be effected continuously about 94-96%. 45 without the application of external heating and The gases evolved from the surface of the cooling means. Other objects will appear herereaction liquid were recovered continuously and inafter. passed through a condenser maintained at a tem- These objects are accomplished according to perature suflicient to condense the water vapor.

the broader aspects of the invention by reacting Sufficient water from the condenser was returned 50 together an alkyl alcohol and a hydrogen halide to the reaction zone to maintain the volume of the such as, for example, hydrogen chloride, in the reaction mixture constant. presence of anaqueous metal halide solution while The yields of ethyl chloride obtained as demaintaining the volume and concentration of scribed in the 'oregoing examples were substansaid metal halide solution constant and below tially higher than y elds obtained in runs at cor- 55 responding temperatures without adding water to the catalyst solution. Furthermore, the procedures described in the examples were effected without external heating or coolingj' whereas procedures in which the catalyst solution were allowed to reach the equilibrium concentrations (that is, no water was added) required external cooling to maintain the desired reaction temperature.

In practicing the invention, it is immaterial from what source the water to be added to the catalyst solution is obtained. The advantage of condensing water from the reaction products rather than adding fresh water to the catalyst solution will be apparent, however, in that the returned condensate carries back into the reaction zone at least a portion of the unreacted materials which have passed through the catalyst mass. I

Any suitable method may be employed in regulating the amount of water returned to the catalyst solution. In operating the process we have found it to be very desirable to regulate the volume of water returned to the catalyst by conductivity measurements made by means of carbon electrodes inserted into the catalyst solution, a difference in liquid level being indicated by a change in the conductivity of such electrodes when an alternating current'is passed through them. In this manner it is possible to control with suflicient accuracy the concentration of the catalyst solution.

While the process is particularly valuable for the production of ethyl chloride, very desirable results are obtained in the preparation of methyl and propyl chlorides from the corresponding alcohols. Alkyl halides such as methyl, ethyl, and propyl bromides may be obtained in a similar manner.

In accordance with the invention certain metal halides other than zinc chlorides may be used satisfactorily as catalysts. Mention may be made of the particular suitability of ferric chloride, antimony chloride and bismuth chloride. The most desirable concentration of the catalyst solution may vary widely depending largely upon the nature of the metal halide catalyst and the re-- actants, the desired products and the temperature at which optimum yields are obtained. When zinc chloride is the metal halide employed, the concentration of the aqueous zinc chloride solution should preferably be about 68-73% by weight, which corresponds to a specific gravity at 25 of about 1.87-1.95.

The temperature of operation may vary within relatively wide limits depending largely upon the particular reactants, catalysts, and results desired. In general, the reaction temperature should be below that giving rise to decomposition of the reactants and reaction products. The reaction of hydrogen chloride and ethyl alcohol, in the presence of zinc chloride, as herein described, is preferably carried out at a temperature within the range of -150 C. and especially desirable results have been obtained in operating the process at temperatures of about -140 C.

The pressure under which the reaction of the hydrogen halide and alcohol is conducted is subject to relatively wide variation. Generally speaking, it is preferable to operate at atmospheric pressure but good results are obtained by operating under superatmospheric pressures.

The proportions of hydrogen halide and alkyl alcohol employed may vary widely but should preferably correspond to at least one molecular equivalent of hydrogen halide for each molecular equivalent of alcohol. Ingeneral, it is preferable to employ about 10-50% hydrogen halide in excess of the stoichiometrically equivalent proportions of alcohol. In the production of ethyl chloride, the hydrogen chloride gas introduced into the catalyst solution may contain impurities such as, for example, air and hydrogen but should, preferably have a purity greater than about 95%.

It will be understood throughout the specification and claims that by the expression equilibrium concentration is meant the concentration which the catalyst solution attains when in dynamic equilibrium with the alcohol and hydrogen halide at reaction temperature.

A particulan'advantage of the invention is that by its application ethyl chloride may be produced by an autothermal' reaction since it is possible to preserve the dilution of the catalyst solution to the preferred concentration and still maintain the temperature thereof at or slightly above 135 C. without external heating or cooling. The process is further advantageous in that the yields based upon the quantities of raw materials treated are relatively high, even at high rates of production. Furthermore, the process is readily controlled and does not require a large amount of equipment and space for its operation.

.{ls many apparent and widely different embodiments of this invention may be made without departing from the'spirit thereof, it is to be understood that we do notlimit ourselves to the foregoing examples or description except as in dicated in the following claims.

We claim:

1. The process of producing an alkyl. halide which comprises reacting'an alkyl alcohol with a hydrogen halide in the presence of a solution of a metal halide catalyst for the reaction,'maintained at reaction temperature and having a concentration below the equilibrium concentration having a concentration below its equilibrium concentration at the reaction temperature;

3. In a process of producing an alkyl chloride, the step which comprises passing a vapor mixture containing an alkyl alcohol and hydrogen chloride into an aqueous metal chloride solution capable of promoting reaction between said alcohol and said hydrogen chloride at a temperature between 110 and C. and maintaining the volume and concentration of said metal chloride solution substantially constant but substantially below the equilibrium concentration at the reaction temperature by adding water thereto.

4. In a process of producing an alkyl chloride, the step which comprises passing a vapor mixture containing alcohol and hydrogen chloride into an aqueous zinc chloride solution maintained at a chloride in the presence of an aqueous zinc chloride solution, the improvement which comprises maintaining the zinc chloride solution at a concentration of about (58-73%.

6. In a process of producing ethyl chloride by the reaction of ethyl alcohol and hydrogen chloride in the presence of an aqueous zinc chloride solution, the improvement which comprises maintaining the zinc chloride solution at a concentration of about 68-73%.

7. The process of producing ethyl chloride which comprises reacting together ethyl alcohol and hydrogen chloride at a temperature of about 135-140 C. in an aqueous solution of zinc chloride maintained at a concentration of about 68- 73%.

8. The process of producing ethyl chloride which comprises reacting together ethyl alcohol and hydrogen chloride in proportions corresponding to at least one mole of hydrogen chloride per mole of alcohol in the presence of an aqueous zinc chloride solution and at a temperature within the range of about 1l0-150 C., removing the water vapor and ethyl chloride evolved, and maintaining the cencentration of the zinc chloride solution at about 68-73% by condensing at least a part of the evolved water-and returning it to said solution.

9. The process of producing ethyl chloride which comprises reacting together ethyl alcohol and hydrogen chloride in proportions corresponding to at least one mole of hydrogen chloride per mole of alcohol in the presence of an aqueous zinc chloride solution and at a temperature of about 135140 C., removing the water vapor and ethyl chloride evolved, and maintaining the concentration of the zinc chloride solution at about Gil-73% by condensing at least a part of the evolved water and returning it to said solution.

10. The process of producing ethyl chloride which comprises simultaneously. passing vaporous ethyl alcohol and at least a molecular equivalent quantity of hydrogen chloride into an aqueous solution of zinc chloride of 68-73% concentration maintained at a temperature of about 135 C., continuously removing the water vapor and ethyl chloride evolved and maintaining the said concentration of the zinc chloride solution by condensing a portion of the evolved water and returning it to the reaction zone.

11. The process of producing an alkyl chloride having less than four carbon atoms, which comprises reacting an alkyl alcohol having less than four carbon atoms with hydrogen chloride in the presence of a solution of zinc chloride maintained at reaction temperature and having a concentration below the equilibrium concentration at said temperature.

12. The process of producing alkyl chlorides having less than four carbon atoms, which comprises reacting together an alkyl alcohol having less than four carbon atoms and hydrogen chloride at a temperature of about 135 C. to about 140 C. in an aqueous solution of zinc chloride maintained at a concentration of about 68% to about 73%.

13. The process of producing an alkyl chloride having less than four carbon atoms, which comprises reacting together an alkyl alcohol having less than four carbon atoms and hydrogen chloride in proportions corresponding to at least one mole of hydrogen chloride per mole of alcohol, in the presence of an aqueous zinc chloride solution and at a temperature within the range of about 110 C. to about 150 C., removing the water vapor and alkyl chloride evolved, and maintaining the concentration of the zinc chloride solution at about 68% to about 73% by condensing at least a part of the evolved water and returning it to said solution.

14. The process of producing an alkyl chloride having less than four carbon atoms, which comprises reacting together an alkyl alcohol having less than four carbon atoms and hydrogen chloride in proportions corresponding to at Ieastone mole of hydrogen chloride per mole of alcohol, in

the presence of an aqueous zinc chloride solution LEE CONE HOLT. HERBERT WILKENS DAUDT. 

